Production process and production apparatus for polybutylene terephthalate

ABSTRACT

An apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid with a glycol, thereby producing an oligomer, a second reactor for polycondensating the oligomer, thereby preparing a low polymerization product, and a third reactor for further polycondensating the low polymerization product, thereby producing a high molecular weight polyester, where the second reactor is a vertical, cylindrical polymerization vessel having a plurality of concentrical partitioned reaction compartments therein, each of the reaction compartments being provided with stirring blades and a heater, and an outlet for volatile matters being provided at the upper part of the vessel. The second reactor contributes to efficient and continuous production of polybutylene terephthalate having a good quality.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a process and an apparatus forcontinuously producing polyester type polymers such as polybutyleneterephthalate and polyethylene terephthalate.

2) Related Art

Since polyethylene terephthalate (hereinafter referred to as PBT) resinsare excellent in the crystallizing characteristic and also excellent inmechanical properties, electric characteristics and heat resistance,they have been used for applications such as electric machines,electronic parts, mechanical parts and automobiles and their demand hasbeen increased steadily.

Heretofore, for the general PBT production process, a terephthalic acidalkyl ester comprising dimethyl terephthalate as a main ingredient and aglycol comprising 1,4-butanediol (hereinafter referred to as BD) as amain ingredient are placed at an appropriate ratio in a mixing vessel, atransesterification catalyst is added and conditioned and then they aresent to a transesterfication reaction vessel set to a predeterminedreaction temperature by a pump. In the transesterification reaction, twoor three stirring vessels with stirring blades are disposed in seriesand methanol formed as reaction by-products, and tetrahydrofuran(hereinafter referred to as THF) formed by decomposition of the methanolformed as reaction by-products and BD and water are separated in adistillation tower. Then, a polymerization catalyst is added and theprocess proceeds to the polymerizing reaction step. At first, verticalstirring vessels or horizontal stirring vessels are disposed inplurality for the prepolymerization step and, further, a horizontalstirring vessel is disposed as a final polymerization step.

For continuous polycondensation process for polyethylene terephthalate,etc. in a relatively low viscosity range, operated under subatmosphericpressure, a plurality multi-tray type, columnar reactors or a pluralityof vertical complete mixing type stirring vessels are used in series asdisclosed in JP-A-48-7090. Oligomers of low polymerization degreesformed by esterification reaction or transesterication reaction arecontinuously fed to one end of such reactors to successively proceed thepolycondensation reaction down to the downstream tray or whiletransferring the oligomers from one stirring vessel to another.

In this connection, the present inventors proposed an apparatus forcontinuously producing polybutylene terephthalate, which comprises afirst reactor for reacting an aromatic dicarboxylic acid comprisingterephthalic acid as a main ingredient or a derivative thereof with aglycol comprising 1,4-butanediol as a main ingredient, thereby producingan oligomer with an average degree of polymerization of 2.2 to 5, asecond reactor for polycondensating the oligomer from the first reactor,thereby preparing a low polymerization product with an average degree ofpolymerization of 25 to 40, and a third reactor for furtherpolycondensating the low polymerization product from the second reactor,thereby producing a high molecular weight polyester with an averagedegree of polymerization of 70 to 130, or further a fourth reactor forfurther polycondensing the polyester from the third reactor to anaverage degree of polymerization of 150 to 200, thereby producing a highmolecular weight polyester with good heat stability and excellenthydrolysis resistance, reactors without any stirrers by an externalpower source being used for the first and second reactors (U.S. patentapplication Ser. No. 09/642587), parts of which are incorporated hereinby reference.

In the apparatus, the second reactor is an approximately cylindricalvessel type, flow reactor in a double cylinder structure having an innercylinder opening in the vessel and an inlet for the process solution atthe lower part of the double cylinder structure, the process solutionpassing through tubes of a shell and tube type heat exchanger providedon the outside of the inner cylinder of the double cylinder structureand thereby heated to a predetermined temperature and passed upwardly tothe level of the inner cylinder opening and then flowing down throughthe inner cylinder while the process solution is stirred with aplurality of doughnut-type trays provided on the inside wall of theouter cylinder, and the vessel is provided with an outlet for volatilematters and reaction by-products at the upper part thereof. The presentinventors have found that short pass and thermal decomposition reactionof the process solution admit of improvement.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and amethod for producing polybutylene terephthalate of good qualityefficiently and continuously by providing a plurality of partitionedreaction compartments in the second reactor, each of the reactioncompartments being stirred and heated to attain complete mixing, therebyeliminating short pass and thermal decomposition reaction of the processsolution.

The object of the present invention can be attained by using, for thesecond reactor, a vertical cylindrical polymerization vessel having aplurality of concentrical partitioned reaction compartments therein,each of the reaction compartments being provided with stirring bladesand a heater, and an outlet for volalite matters being provided at theupper part of the vessel, where polycondensation reaction is efficientlycarried out, while the process solution to be treated in the reactioncompartments is successively transferred radially and inwardly from theouter reaction compartment to the inner one, whereby preventingoccurrence of thermal decomposition reaction and degradation of productquality.

(1) An apparatus for continuously producing polybutylene terephthalate,which comprises a first reactor for reacting an aromatic dicarboxylicacid comprising terephthalic acid as a main ingredient or a derivativethereof with a glycol comprising 1,4-butanediol as a main ingredient,thereby producing an oligomer with an average degree of polymerizationof 2 to 5; a second reactor for polycondensating the oligomer from thefirst reactor, thereby preparing a low polymerization product with a lowdegree of polymerization; and a third reactor for furtherpolycondensating the low polymerization product from the second reactor,thereby producing a high molecular weight polyester with an averagedegree polymerization of 70 to 180, or an apparatus for continuouslyproducing polybutylene terephthalate, which comprises a first reactorfor reacting an aromatic dicarboxylic acid comprising terephthalic acidas a main ingredient or a derivative thereof with a glycol comprising1,4-butanediol as a main ingredient, thereby producing an oligomer withan average degree of polymerization of 2 to 5, a second reactor forpolycondensating the oligomer from the first reactor, thereby preparinga low polymerization product with a low degree of polymerization; athird reactor for further polycondensating the low polymerizationproduct from the second reactor, thereby producing a high molecularweight polyester with an average degree polymerization of 70 to 130; anda fourth reactor for further polycondensing the polyester from the thirdreactor to an average degree of polymerization of 150 to 200, therebyproducing a high molecular weight polyester, characterized in that (i)the first reactor is an approximately cylindrical vessel type reactorhaving an inlet and an outlet for a process solution at lower parts,respectively, of the vessel proper and an outlet for volatile mattersand reaction by-products at the upper part of the vessel proper, andhaving a calandria type heat exchanger formed in the longitudinaldirection of the vessel proper and near the inside wall of the vesselproper and being immersed in the process solution, the process solutionsupplied into the vessel proper at the inlet at the lower part thereofis heated to a predetermined reaction temperature by the heat exchangerand is stirred and mixed by spontaneous convection due to a densitydifference caused by a temperature difference between the formedvolatile by-product gas and the process solution, (ii) the secondreactor is a vertical cylindrical polymerization vessel having aplurality of concentrated partitioned reaction compartments therein,each of the reaction compartments being provided with stirring bladesand a heater, and an outlet for volatile matters being provided at theupper part of the vessel, (iii) the third reactor is a horizontalcylindrical vessel type reactor having an inlet and an outlet for aprocess solution at lower parts on one end and an another end in thelongitudinal direction of the vessel proper, respectively, and an outletfor volatile matters at the upper part of the vessel proper, and astirring rotor rotating in the proximity of the inside wall of thevessel proper is provided in the longitudinal direction of the vesselproper, the stirring rotor in the vessel proper is provided with aplurality of stirring blade blocks in accordance with the viscosity ofthe process solution and the stirring blades are without any rotatingshaft along the center of the stirring rotor, and (iv) the fourthreactor is a horizontal, approximately cylindrical vessel type reactorhaving an inlet and an outlet for a process solution at lower parts anone end and an another end in the longitudinal direction of the vesselproper, respectively, and an outlet for volatile matters at the upperpart of the vessel proper, the reactor has two stirring rotors rotatingin the proximity of the inside wall of the vessel proper in thelongitudinal direction of the vessel proper, and the rotors each havestirring blades.

In the second reactor, each of the stirring blades can be fixed to onecommon half-length rotating shaft.

The second reactor can be a vertical cylindrical polymerization vesselhaving two partitioned concentrical reaction compartments therein eachof reaction compartments being provided with stirring blades and aheating coil, the stirring blades being fixed to one common half-lengthrotating shaft connected to a driving means mounted on the upper part ofthe vessel proper, and an outlet for volatile matters being provided atthe upper part of the vessel, or can be a vertical cylindricalpolymerization vessel having two partitioned concentrical reactioncompartments therein, the stirring blades provided in the inner reactioncompartment is without any counterpart rotating shaft along the rotationcenter.

The term “one common, half-length rotating shaft” herein used means acommon rotating shaft whose lower end locates above the central reactioncompartment without extending into the central reaction compartment. Inother words, the stirring blades in the central reaction compartment arewithout any counterpart rotating shaft therein. Typical embodiments ofthe present invention are summarized below.

(2) A process for continuously producing polybutylene terephthalate,which comprises producing an oligomer with an average degree ofpolymerization of 2 to 5 by reaction of an aromatic dicarboxylic acidcomprising terephthalic acid as a main ingredient or a derivativethereof with a glycol comprising 1,4-butanediol as a main ingredient andthen polycondensing the oligomer in series of a plurality of reactors,thereby producing a polymer of a low degree of polymerization and a highmolecular weight polyester, characterized in that production of polymerof a low degree of polymerization by polycondensation of the oligomer iscarried out in a vertical cylindrical polymerization vessel (initialpolymerization vessel) containing a plurality of partitionedconcentrical reaction compartments therein, each of the reactioncompartments being provided with stirring blades and a heater, and anoutlet for volatile matters being provided at the upper part of thevessel, the polycondensation reaction can be efficiently carried out,while a process solution (oligomer) to be treated in the reactioncompartments is successively transferred radially and inwardly from theouter reaction compartment to the inner one, and more specifically, aprocess for continuously producing polybutylene terephthalate, whichcomprises a first step of reacting an aromatic dicarboxylic acidcomprising terephthalic acid as a main ingredient or a derivativethereof with a glycol comprising 1,4-butanediol as a main ingredient ina first reactor, thereby producing an oligomer with an average degree ofpolymerization of 2 to 5, a second step of polycondensing the oligomerfrom the first step in a second reactor, thereby preparing a lowpolymerization product with an average degree of polymerization of 20 to70, a third step of further polycondensing the low polymerizationproduct from the second step in a third reactor, thereby producing ahigh molecular weight polyester with an average degree of polymerizationof 70 to 180, or a process for continuously producing polybutyleneterephthalate, which comprises a first step of reacting an aromaticdicarboxylic acid comprising terephthalic acid as a main ingredient or aderivative thereof with a glycol comprising 1,4-butanediol as a mainingredient in a first reactor, thereby producing an oligomer with anaverage degree of polymerization of 2 to 5, a second step ofpolycondensing the oligomer from the first step in a second reactor,thereby preparing a low polymerization product with an average degree ofpolymerization of 20 to 70, a third step of further polycondensing thelow polymerization product from the second step in a third reactor,thereby producing a high molecular weight polyester with an averagedegree of polymerization of 70 to 130, and a fourth step of furtherpolycondensing the polyester from the third step in a fourth reactor,thereby producing a high molecular weight polyester with an averagedegree of polymerization of 150 to 200, characterized in that reactorscharacterized by (i), (ii), (iii), and (iv) described in the foregoing(1) are used; the aromatic dicarboxylic acid comprising terephthalicacid as a main ingredient or a derivative thereof and the glycolcomprising 1,4-butanediol as a main ingredient are supplied to the firststep in a molar ratio of the former to the latter of 1:1.7 to 1:3.0, andthe first step is carried out at 220°-250° C. and 33 kPa-150 kPa, thesecond step at 230°-255° C. and 0.5 kPa-20 kPa and the third and fourthstep each at 230°-255° C. and 0.665 kPa-0.067 kPa; the stirring bladesof the second reactor is rotated in a range of 5 ppm-100 ppm; thestirring blades of the third and fourth reactors are rotated in a rangeof 0.5 rpm-10 rpm; total reaction time for the first to the third stepsis in a range of 4-7.5 hours, or total reaction time for the first tothe fourth step is in a range of 6 to 8.5 hours; a slurry of thearomatic dicarboxylic acid comprising terephthalic acid as a mainingredient or a derivative thereof and the glycol comprising1,4-butanediol as a main ingredient prepared in a ratio of the former tothe latter of 1:1.7 to 1:3.0 is supplied to the first step uponadmixture of an esterifying catalyst or a polymerization reactioncatalyst; and another third reactor or a plurality of third reactors isprovided in parallel to the third reactor in the third step, therebyproducing different kinds of polybutylene phthalate with differentdegrees of polymerization from that produced in the main line of thethird and fourth reactors or adjusting operating conditions of each of aplurality of the third reactors to increase kinds, precise qualitycontrol and production rate of polybutylene terephthalate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an apparatus layout in a process for continuously producingPBT according to one embodiment of the present invention.

FIG. 2 shows an apparatus layout in a process for continuously producingPBT according to another embodiment of the present invention.

FIG. 3 shows an apparatus layout in a process for continuously producingPBT according to other embodiment of the present invention.

FIG. 4 is a vertical cross-sectional front view showing a second reactor(initial polymerization vessel) according to one embodiment of thepresent invention.

FIG. 5 is a horizontal cross-sectional view along the line A—A of FIG.4.

FIG. 6 is a vertical cross-sectional front view showing a second reactor(initial polymerization vessel) according to another embodiment of thepresent invention.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows an embodiment of this invention.

FIG. 1 is an apparatus layout of a process for continuously for theproducing PBT according to this invention. Since a direct esterifyingprocess is very advantageous from an economical point of view as anindustrial process for producing a polyester, the direct esterifyingprocess has been often adopted recently for the production ofpolyesters. In FIG. 1, reference numeral 1 denotes a starting materialconditioning vessel for mixing and stirring TPA and BD as the startingmaterials for PBT in a predetermined ratio. In the process, apolymerizing reaction catalyst or additives such as a stabilizer or aquality controller are sometimes added in this step and, in thisembodiment, the polymerizing reaction catalyst or the additive ischarged to starting material supply line 2 just before the inlet of anesterifying reaction vessel from catalyst supply line 10 and supplied tothe esterifying reaction vessel. The polymerizing reaction catalyst caninclude metal compounds such as organic titanium, organic tin, organiczirconia, etc. and it is well known the reaction rate depends on thekind and the combination of the catalyst to be used, as well as theygive a significant effect on the quality such as hue and the heatstability of the resultant PBT. In particular, it is well known that thecatalyst of the organic titanium compound is influenced with the ambientmoisture to decrease the catalytic effect. In order to minimize theeffect, the catalyst is added to the point just before the inlet of theesterifying reaction vessel in this embodiment. Since this can minimizethe rate of deactivation of the added catalyst, it is possible todecrease the amount of the catalyst charged and produce a resin of goodhue. Further, since the reactions are carried out in the presence of thecatalyst at high temperature for a long time, various side-reactionstake place to color the polymerization product, increase the THF contentor the terminal carboxyl group concentration to higher than theappropriate values, thereby deteriorating the quality of PBT or loweringthe physical properties such as the strength, etc. While a developmentfor new catalyst has been attempted for improving such problems, organictitanium used most frequently at present in the industry is excellent inview of the cost and the performance. However, the resultant polyesterpolymer product is inevitably colored even when the catalyst is used.Therefore, improvement has been attempted by the combined use of aphosphorus type stabilizer (for example, phosphoric acid, trimethylphosphate, triphenyl phosphate, etc.) as the stabilizer. Further, inanother process the quality is stabilized by modifying the position forcharging the polymerization catalyst and the stabilizer. Preferably, inthe ordinary process, the amount of the catalyst used is from 20 to 100ppm in terms of metallic titanium concentration and the amount of thestabilizer used is from 0 to 600 ppm in terms of metallic phosphorusconcentration, if required.

The starting material and the catalyst prepared as described above aresupplied to the first esterifying reaction vessel 3 through supply line2 for supplying the starting material and through catalyst addition line10 for the catalyst prepared separately, which joins supply line 2,respectively. The outside of the esterifying reaction vessel (firstreactor) 3 is in a jacket structure (not illustrated) to keep theprocess solution at the reaction temperature, calandria type heatexchanger 4 is disposed in the solution as a solution heating unit,thereby heating the process solution flowing in the tubes by an externalheat source, thereby conducting the reaction while circulating theinternal solution only by the spontaneous circulation due to asynergistic effect between the change of the density caused by thevolatile gas formed in the esterifying reaction step and the temperaturedifference. The most desired type of reactor 3 is a calandria type forspontaneously circulating the process solution in the reactor byutilizing the spontaneous evaporating action of side reaction productsformed by the esterifying reaction. Since the reactor of this type doesnot require an external stirring power source, it has a merit that theapparatus layout can be simplified, a shaft sealing device for astirring shaft is no more required and the fabrication cost of thereactor is reduced. As an example of such reactor, a device as shown inJP-A-108-5501 is desirable. However, the present invention is notlimited to such a device, and it is not objectionable to use a reactorhaving a stirring blade for a process reason. In first reactor 3, waterformed by reaction takes a steams form, which makes gas phase 5 togetherwith gasified BD vapors and by-produced THF vapors. A temperature from220° C. to 250° C. and a subatmospheric pressure or slightlysuperatmospheric pressure are preferable conditions. In particular as tothe pressure condition, an optimum pressure condition is determined inaccordance with BD-TPA molar ratio of the starting materials(hereinafter referred to as B/T). In B/T=2.0 or higher, the BDconcentration in the process solution can be ensured even under apressure higher than the atmospheric pressure, the desired esterifyingratio can be reached within a predetermined residence time. However, inB/T=less than 2.0, the esterifying ratio is lowered to increase thereaction load in the subsequent polymerization steps and bring about aproblem of causing disadvantage in a vacuum system and auxiliariesrelevant thereto. Accordingly, at B/T=less than 2.0, it is effective toset the reaction pressure to a subatmospheric pressure. The pressurereduction can lower the boiling point of BD and lower the reactiontemperature. Usually, the reaction rate lowers when the reactiontemperature is lowered, but in the spontaneous circulation type reactorof such a structure as in this embodiment, the pressure reductionincreases the reaction by-product gas volume to improve the circulatingperformance within the reactor and give an effect on the improvement ofthe reaction condition. Further, the pressure reduction can also improvethe leaving rate of moisture as a by-product of the esterifying reactionand make a forward reaction rate constant larger. Further, the effectson shortening the esterifying reaction time and decreasing the amount ofTHF as the side-reaction product become remarkable by the improvement inthe esterifying reaction rate with a synergistic effect on lowering thereaction temperature, and thus the amount of THF formed can be reducedremarkably.

Preferable reaction temperature in this case is from 220° C. to 250° C.and, particularly, under subatmospheric pressure of 50 to 80 kPa, theresidence time of 1.5 to 2.4 hrs and reaction temperature of 225° C. to230° C. are remarkably effective for the improvement of the esterifyingreaction rate and the decrease of the amount of THF formed. The amountof THF formed in this case is about 15 to 25 mol%/h in terms of molarfraction of the starting material TPA. The gas of the gas phase zone 5as a volatile component leaving the process solution is separated intowater, THF and BD by a distillation column (not shown) disposed abovefirst esterifying reaction vessel 3. Water and THF are removed from thesystem, and BD is returned through a purification step etc. again intothe system or as the starting material to BD tank 33 from the bottom ofthe distillation column through BD recycle line 35. The recycle BD issupplied to starting material conditioning vessel 1 from BD tank 33through BD supply line 34, and the recycle BD in BD tank 33 is subjectedto purify adjustment of the starting material BD by BD purificationtreatment (not shown), if required. Furthermore, the recycle BDdischarged from wet condensers (not shown) at pressure reduction devicesdisposed at initial polymerization vessel 14 and final polymerizer 18 isreturned to BD tank 33 through BD recycle line 36 to further improve theBD unit. In that case, fresh BD is supplied to the wet condenser atfinal polymerizer 18 through fresh BD supply line 39, then to the wetcondenser at initial polymerization vessel 14 through BD recycle line37, and to BD tank 33 through BD recycle line 36.

The process solution reaching a predetermined esterifying ratio inesterifying reaction vessel 3 is supplied through connection pipe 6 toinitial polymerization vessel (second reactor) 14. Control valve 7 isdisposed to adjust the flow rate of the process solution at the midwayof connection pipe 6. Valve 7 controls the first reactor to a constantliquid level and keeps a constant reaction time. The process solution,when reached a predetermined esterifying ratio in esterifying reactionvessel 3, is supplied to initial polymerization vessel (second reactor)14 by oligomer pump 12 disposed in the midway of connection pipe 11.

FIG. 4 and FIG. 5 show a second reactor (initial polymerization vessel)according to one embodiment of the present invention, where FIG. 4 is avertical cross-sectional front view and FIG. 5 is a horizontalcross-sectional view along the line A-A of FIG. 4.

In FIG. 4, numeral 14 denotes a vertical cylindrical closed vesselproper, whose outside is covered with heating medium jacket 402, androtating shaft 403 and driving means 404 are provided at the upper partof the center of vessel proper 14. Vessel proper 14 has two concentricalcompartments partitioned by partitioning cylinder 405 therein, that is,doughnut-type first compartment 406 and cylindrical second compartment407. Stirring blades 408 and 409 for stirring said first and secondcompartments 406 and 407, respectively, by rotation are fixed to onecommon, half-length rotating shaft 403, that is, a rotating shaft whoselower end of a locates above second compartment 407 without extendinginto second compartment 407. Furthermore, heating tubular coils 410 and411 are provided at the outsides of stirring blades 408 and 409 in.first compartment and second compartment 406 and 407, respectively.Heating medium inlet nozzles 412 and 413 and heating tubular coils 410and 411, respectively, are provided through vessel proper 14. At thelower part of first compartment 406 of vessel proper 14 is providedprocess solution inlet nozzle 416 while at the lower part at the centerof second compartment 407 of vessel proper 14 is provided processsolution outlet nozzle 417. Furthermore, outlet nozzle 418 for volatilematters is provided at the upper part of vessel proper 14 and isconnected to a condenser and an evacuator through a piping (not shown inthe drawing). 419 and 420 denote heating medium inlet and outlet,respectively, to and from heating medium jacket 402.

Stirring blades 408 in first compartment 406 rotate at a higherperipheral speed than stirring blades 409 in second compartment 407rotate, and thus the process solution in first compartment 406 isstirred in a slim state of low stirring resistance, whereas the processsolution in second compartment 407 is stirred in a broad state of highstirring resistance because of lower peripheral speed of stirring blades409 in second compartment 407, whereby stirring blades 408 and 409,which rotate at the same rpm, can give the same level of stirring effectin first and second compartments 406 and 407. Furthermore, stirringblades 409 is without any counterpart rotating shaft at the rotatingcenter in second compartment 407, and thus there is no fear at all ofdeposition of the process solution onto the rotating shaft and theresulting deterioration thereon.

In the second reactor, the process solution continuously fed throughinlet nozzle 416 enters at first compartment 406, heated by heatingtubular coil 410 and stirred by stirring blades 408 while proceedingwith polycondensation reaction, and the generated volatile matters suchas 1,4-butanediol, etc. are evaporated and trapped by a condenser (notshown in the drawing) through outlet nozzle 418 for volatile matters.The reaction-proceeded process solution enters second compartment 407over the upper edge of partition cylinder 405 from first compartment406. The process solution is also heated by heating tubular coil 411 andstirred by stirring blades 409 in second compartment 407 in the samemanner as in first compartment 406, while further proceeding with thepolycondensation reaction. The generated volatile matters such as1,4-butanediol, etc. are evaporated and trapped by the condenser throughoutlet nozzle 418.

The reaction-proceeded process solution is led to successive finalpolymerizer 18 from the lower part of second compartment 407 throughoutlet nozzle 417 for the process solution. The polycondensationreaction of the process solution proceeds efficiently in a completemixing state in both two first and second compartments 406 and 407 invessel proper 14 without any short pass or without any thermaldecomposition in both two first and second compartments 406 and 407because of any provion of closed connection tubes between the twocompartments. Thus, the second reactor can contribute to continuousproduction of high quality polybutylene terephthalate polymerizationproducts.

In the polycondensation reaction of polybutylene terephthalate in thesecond reactor, bishydroxybutyl terephthalate having an average degreeof polymerization of 2 to 5 is continuously fed to vessel proper 14through inlet nozzle 416 to proceed with polycondensation reaction,while separating generated 1,4-butandediol and water vapors withinvessel proper 14, and polymerization products of polybutyleneterephthalate having an average degree of polymerization of 20 to 70 canbe obtained. The generated volatile matters such as 1,4-butanediol, etc.are discharged through outlet nozzle 418 for volatile matters. Thesecond reactor is operated under the following conditions: liquidtemperature: 230°-255° C., pressure: 0.5 to 20 kPa; rotation of stirringblades: 5-100 rpm.

According to another embodiment of the present invention, as shown inFIG. 6, vessel proper 14 has three compartments partitioned by twopartitioning cylinders 405A and 405B, that is, doughnut-shaped firstcompartment 406A, doughnut-shaped second compartment 406B, andcylindrical third compartment 407C therein, and stirring blades 408A,408B and 409C, which stir first compartment 406A, second compartment406B and third compartment 407C by rotation, respectively, are fixed toone common, half-length rotating shaft 403. Heating tubular coils 410A,410B and 411C are provided in first, second and third compartments 406A,406B and 407C, respectively. In this embodiment, the process solutionenters first compartment 406A through inlet nozzle 416 at the side ofvessel proper 14 and enters second compartment 406B through theclearance between the lower edge of partitioning cylinder 405A and thebottom of vessel proper 14, then enters third compartment 407C over theupper edge of partitioning cylinder 405B and leaves vessel proper 14through outlet nozzle 417 for the process solution at the lower part ofthird compartment 407C.

In this embodiment, vessel proper 14 act as three complete mixingvessels, and thus can proceed with polycondensation reaction for ashorter time, and can contribute to continuous production ofpolymerization products of polybutylene terephthalate with betterquality and less heat degradation.

The process solution after a predetermined residence time (reactiontime) in initial polymerization vessel (second reactor) 14 is suppliedthrough connection pipe 17 to final polymerizer (third reactor) 18. Inthe final polymerizer, polymer of desired polymerization degree isproduced by further polycondensating reaction, while undergoing a goodsurface renewing effect by stirring blades 19 with no stirring centershaft driven by external power source 21, thereby increasing the degreeof polymerization. A suitable apparatus for the final polymerizer (thirdreactor) is an apparatus disclosed in JP-A-10-77348 from the viewpointof the surface renewing effect and the power consumption characteristic.The reaction is conducted to a degree of polymerization of about toabout 130 in this case under such reaction conditions as 230° C. to 255°C. and a pressure of 0.665 kPa to 0.067 kPa. Polycondensation has beenso far carried out in two vessels due to a wide range of viscosity ofthe process solution, the present final polymerizer can carry outpolycondensation in a single unit, thereby greatly reducing theapparatus cost. Total residence time for the first to third reactors is4-7.5 hours but from the viewpoint of the quality, the residence timethroughout the entire polymerizing steps is preferably in a range from 2to 4 hours. Further, the residence time can be made longer by adjustingthe temperature and the pressure, if required, and, for example, in caseof reducing the production rate to minimize the quality fluctuation. Inparticular, to keep an acid value of polymer as one of PBT evaluationitems as low as possible, it is desirable that the reaction temperatureis 250° C. or lower.

When PBT is produced continuously according to the foregoing apparatuslayout, the number of reactors is decreased, as compared with theconventional apparatus layout, and thus the apparatus fabrication costcan be reduced, and the number of distillation columns and condensersrelevant to the apparatus can be also reduced due to the decrease in thenumber of the apparatus units. Their connection piping, instrumentationparts and valves can be omitted largely, and utility costs forevacuation means, heating medium means are greatly reduced as well,thereby lowering the running cost as another advantage.

Further, to obtain PBT of higher intrinsic viscosity (IV) another finalpolymerizer (fourth reactor) can be provided after final polymerizer(third reactor) 18. This embodiment is shown in FIG. 2. Apparatus layoutand functions of first, second and third reactors are the same asdescribed above, referring to FIG. 1 and thus their description is to beomitted below. Fresh BD is supplied to a wet condenser at fourth reactor23 and then through BD recycle line 38 to the wet condenser at thirdreactor 23, followed by the same functions as in the embodiment of FIG.1. Process solution 20 having a degree of polymerization of about 70 toabout 130 obtained in the third reactor is supplied to fourth reactor 23by polymer pump 22 at the midway of the connection pipe between thirdreactor 18 and fourth reactor 23. Since the process solution has such ahigh viscosity as a few hundred kPas in fourth reactor 23, the samestirring device as used in third reactor 18 is no more used, because arotation phenomenon, i.e. attachment and staying of the process solutionon rotating stirring blades, occurs. That is, a reactor with a stirringdevice for a high viscosity solution must be used. A suitable reactor isa biaxial reactor for high viscosity solution treatment as disclosed inJP-B-6-21159 and JP-A-48-102894.

In this embodiment, description will be made below, referring to abinocular spectacle rim-type polymerizer disclosed in JP-A-48-102894(Japanese Patent No. 1024745), but the present invention will not belimited thereto. Fourth reactor 23 is a biaxial polymerization reactorwith two stirring shafts each having binocular spectacle rim-typestirring blades 24 as fixed thereto alternately with a phase differenceof 90° and at specific distances therebetween, the two stirring shaftsbeing set to each other alternately with a phase difference of 90 ° anddriven by external power source 25. The process solution supplied fromthe inlet port is pushed and extended outwardly due to the stirringblade rotating action from the center to the outward direction, wherethe process solution undergoes a good surface renewing action, therebyevaporating the volatile components from the inside of the processsolution and promoting the reaction, with the result of further increasein the viscosity. The process solution is then discharged as polymer 24having a higher degree of polymerization. The reaction is conducted to apolymerization degree of about 150 to 200 under such reaction conditionsas temperature of 230° C. to 255° C., pressure of 0.665 kPa to 0.067 kPaand residence time of 0.7 to 1.5 hours.

An embodiment of producing different kinds of polybutyleneterephthalates at the same time will be described below, referring toFIG. 3. The embodiment of FIG. 3 shows disposition of another thirdreactor 26 in parallel to the facility of producing polybutyleneterephthalate with a high degree of polymerization shown in FIG. 2.Fresh BD is supplied to the wet condensers at fourth reactor 23 and atthird reactor 26, respectively, through supply line 39 and finallycollected into BD tank 33 through BD recycle lines 38, 37 and 36, asdescribed in the embodiments of FIG. 1 and FIG. 2, and also through BDrecycle line 40, respectively. Third reactors 18 and 26 will bedescribed below, referring to the reactor as explained in the embodimentof FIG. 1, but the present invention will not be limited to such areactor. The process solution leaving second reactor 14 is divided atthe midway of connection pipe 17 and one portion of the process solutionis led to third reactor 18 through flow control valves 31 and anotherdivided portion of the process solution is led to third reactor 26through branch connection pipe 30 and flow control valve 32,respectively. This embodiment shows the division into two portions ofthe process solution, but the present invention will not be limitedthereto.

The one portion of the process solution is passed through third reactor18 and fourth reactor 23 to produce polybutylene terephthalate with ahigh degree of polymerization. The other divided portion of the processsolution was passed through third reactor 26 to produce polybutyleneterephthalate with a lower degree of polymerization. This series of theproduct polybutylene terephthalates can be produced in any desiredproportion by adjusting flow control valves 31 and 32. A further thirdreactor can be provided, though not shown in the drawing, to produce adifferent kind of polybutylene terephthalate, e.g. with a different acidvalue but the same degree of polymerization or produce polybutyleneterephthalate with a little different degree of polymerization or adjustthe production rate by setting different reaction conditions from thosefor third reactor 26. The stirring blades of the third and fourthreactors are rotated in a range of 0.5 rpm-10 rpm.

According to the present invention, the second reactor can contribute toefficient and continuous production of polybutylene terephthalate havinga good quality by intensively conducting complete mixing of processsolution in at least two partitioned reaction compartments, whiletransferring the process solution from one reaction compartment toanother by overflow or spontaneous flow without using any piping ortransfer means, thereby eliminating occurrence of short pass and thermaldecomposition of the process solution therein.

According to the present invention, the entire apparatus efficiency canbe improved by making an apparatus for continuously producing PBT fromtotal 3 reactors, i.e. one for the direct esterifying step, one for theinitial polymerizing step and one for the final polymerizing step,together with an economical operation of the apparatus due to theresulting energy saving.

Furthermore, according to the present invention, PBT with a high degreeof polymerization can be produced through bulk polymerization by addinga reactor for high viscosity treatment to an apparatus for continuouslyproducing PBT comprising total 3 reactors, i.e. one for the directesterifying step, one for the initial polymerizing step and one for thefinal polymerizing step, together with the energy saving of theapparatus.

Still furthermore, according to the present invention, different kindsof PBT can be produced by dividing the production line following thesecond reactor of an apparatus for continuously producing PBT into aproduction line for higher degree of polymerization and anotherproduction line for a lower degree of polymerization. Yield of suchdifferent kinds of PBT can be adjusted together with economicaloperation of the apparatus for continuously producing PBT.

What is claimed is:
 1. An apparatus for continuously producingpolybutylene terephthalate, which comprises a first reactor for reactingan aromatic dicarboxylic acid comprising terephthalic acid as a mainingredient or a derivative thereof with a glycol comprising1,4-butanediol as a main ingredient, thereby producing an oligomer withan average degree of polymerization of 2 to 5; a second reactor forpolycondensating the oligomer from the first reactor, thereby preparinga low polymerization product with a low degree of polymerization; and athird reactor for further polycondensating the low polymerizationproduct from the second reactor, thereby producing a high molecularweight polyester with an average degree of polymerization of 70 to 180,where the second reactor is a vertical, cylindrical polymerizationvessel having a plurality of concentrical partitioned reactioncompartments therein, each of the reaction compartments being providedwith stirring blades and a heater, and an outlet for volatile mattersbeing provided at the upper part of the vessel.
 2. An apparatus forcontinuously producing polybutylene terephthalate, which comprises afirst reactor for reacting an aromatic dicarboxylic acid comprisingterephthalic acid as a main ingredient or a derivative thereof with aglycol comprising 1,4-butanediol as a main ingredient, thereby producingan oligomer with an average degree of polymerization of 2 to 5, a secondreactor for polycondensating the oligomer from the first reactor,thereby preparing a low polymerization product with a low degree ofpolymerization; a third reactor for further polycondensating the lowpolymerization product from the second reactor, thereby producing a highmolecular weight polyester with an average degree of polymerization of70 to 130; and a fourth reactor for further polycondonsing the polyesterfrom the third reactor, thereby producing a high molecular weightpolyester with an average degree of polymerization of 150 to 200, wherethe second reactor is a vertical cylindrical polymerization vesselhaving a plurality of concentrical partitioned reaction compartmentstherein, each of the reaction compartments being provided with stirringblades and a heater, and an outlet for volatile matters being providedat the upper part of the vessel.
 3. An apparatus according to claim 1 or2, wherein the first reactor is an approximately cylindrical vessel typereactor having an inlet and an outlet for a process solution at lowerparts, respectively, of the vessel proper and an outlet for volatilematters and reaction by-products at the upper part of the vessel proper,and having a calandric type heat exchanger formed in the longitudinaldirection of the vessel proper and near the inside wall of the vesselproper and being immersed in the process solution, the process solutionsupplied into the vessel proper at the inlet at the lower part thereofis heated to a predetermined reaction temperature by the heat exchangerand being stirred and mixed by spontaneous connection due to a densitydifference caused by a temperature difference between the formedvolatile by-product gas and the process solution.
 4. An apparatusaccording to claim 1 or 2, wherein the third reactor is a horizontalcylindrical vessel type reactor having an inlet and an outlet for aprocess solution at lower parts on one end and on another end in thelongitudinal direction of the vessel proper, respectively, and an outletfor volatile matters at the upper part of the vessel proper, and astirring rotor rotating in the proximity of the inside wall of thevessel proper is provided in the longitudinal direction of the vesselproper, the stirring rotor in the vessel proper is provided with aplurality of stirring blade blocks in accordance with the viscosity ofthe process solution, and the stirring blades are without any rotatingshaft along the center of the stirring rotor.
 5. An apparatus accordingto claim 2, wherein the fourth reactor is a horizontal, approximatelycylindrical vessel type reactor having an inlet and an outlet for aprocess solution at lower parts on one end and on another end in thelongitudinal direction of the vessel proper, respectively, and an outletfor volatile matters at the upper part of the vessel proper, the reactorhas two stirring rotors rotating in the proximity of the inside wall ofthe vessel proper in the longitudinal direction of the vessel proper,and the rotors each have stirring blades.
 6. An apparatus according toclaim 1 or 2, wherein the second reactor is a vertical cylindricalvessel having two partitioned concentrical reaction compartmentstherein, each of the reaction chambers being provided with stirringblades and a heating coil, the stirring blades being fixed to onecommon, half length rotating shaft connected to a driving means mountedon the upper part of the vessel, and an outlet for volatile mattersbeing provided at the upper part of the vessel.
 7. An apparatusaccording to claim 1 or 2, wherein the second reactor is a verticalcylindrical vessel having two partitioned reaction compartments therein,the stirring blades provided in the inner reaction compartment arewithout any counterpart rotating shaft along the rotation center.
 8. Anapparatus according to claim 1 or 2, wherein the polymer produced in thesecond reactor has an average degree of polymerization of 20 to
 70. 9. Aprocess for continuously producing polybutylene terephthalate, whichcomprises producing an oligomer with an average degree of polymerizationof 2 to 5 by reaction of an aromatic dicarboxylic acid comprisingterephthalic acid as a main ingredient or a derivative thereof with aglycol comprising 1,4-butanediol as a main ingredient and thanpolycondensing the oligomer in series of a plurality of reactors,thereby producing a polymer of a low degree of polymerization and a highmolecular weight polyester, characterized in that production of polymerof a low degree of polymerization by polycondensation of the oligomer iscarried out in a vertical cylindrical polymerization vessel having aplurality of partitioned concentrical reaction compartments therein,each of the reaction compartments being provided with stirring bladesand a heater, and an outlet for volatile matters being provided at theupper part of the vessel, the polycondensation reaction is efficientlycarried out, while a process solution to be treated in the reactioncompartments is successively transferred radially and inwardly from theouter reaction compartment to the inner one.
 10. A process according toclaim 9, which comprises a first step of reacting an aromaticdicarboxylic acid comprising terephthalic acid as a main ingredient or aderivative thereof with a glycol comprising 1,4-butanediol as a mainingredient in a first reactor, thereby producing an oligomer with anaverage degree of polymerization of 2 to 5, a second step ofpolycondensing the oligomer from the first step in a second reactor,thereby preparing a low polymerization product with an average degree ofpolymerization of 20 to 70, and a third step of further polycondensingthe low polymerization product from the second step in a third reactor,thereby producing a high molecular weight polyester with an averagedegree of polymerization of 70 to 180, where the second reactor is avertical cylindrical polymerization vessel having a plurality ofpartitioned concentrical reaction compartments therein, each of thereaction compartments being provided with stirring blades and a heater,and an outlet for volatile matters being provided at the upper part ofthe vessel, the polycondensation reaction is efficiently carried out,while the process solution to be treated in the reaction compartments issuccessively transferred radially and inwardly from the outer reactioncompartment to the inner one.
 11. A process for according to claim 9,which comprises a first step of reacting an aromatic dicarboxylic acidcomprising terephthalic acid as a main ingredient or a derivativethereof with a glycol comprising 1,4-butanediol as a main ingredient ina first reactor, thereby producing an oligomer with an average degree ofpolymerization of 2 to 5, a second step of polycondensing the oligomerfrom the first step in a second reactor, thereby preparing a lowpolymerization product with an average degree of polymerization of 20 to70, a third step of further polycondensing the low polymerizationproduct from the second step in a third reactor, thereby producing ahigh molecular weight polyester with an average degree of polymerizationof 70 to 130, and a fourth step of further polycondensing the polyesterfrom the third step in a fourth reactor, thereby producing a highmolecular weight polyester with an average degree of polymerization of150 to 200, where the second reactor is a vertical cylindricalpolymerization vessel having a plurality of partitioned concentricalreaction compartments therein, each of the reaction compartments beingprovided with stirring blades and a heater, and an outlet for volatilematters being provided at the upper part of the vessel, thepolycondensation reactor is efficiently carried out, while a processsolution to be treated in the reaction compartments is successivelytransferred radially and inwardly from the outer reaction compartment tothe inner one.
 12. A process according to claim 10 or 11, wherein thesecond step is carried out at a temperature of 230° to 250° C. and apressure of 0.5 to 20 kPa and at 5 to 100 rpm of the stirring blades.13. A process according to claim 10 or 11, wherein the third reactor isa horizontal cylindrical vessel type reactor having an inlet and anoutlet for a process solution at lower parts on one end and on anotherend in the longitudinal direction of the vessel, respectively, and anoutlet for volatile matters at the upper part of the vessel, and astirring rotor rotating in the proximity of the inside wall of thevessel being provided in the longitudinal direction of the vesselproper, the stirring rotor being made of a plurality of stirring bladeblocks in accordance with the viscosity of the process solution, and thestirring blades being without any rotating shaft along the center of thestirring rotor.
 14. A process according to claim 11, wherein the thirdreactor is a horizontal cylindrical vessel type reactor having an inletand an outlet for a process solution at lower parts on one end and ananother end in the longitudinal direction of the vessel proper,respectively, and an outlet for volatile matters at the upper part ofthe vessel proper, and a stirring rotor rotating in the proximity of theinside wall of the vessel is provided in the longitudinal direction ofthe vessel, the stirring rotor in the vessel is provided with aplurality of stirring blade blocks in accordance with the viscosity ofthe process solution and the stirring blades are without any rotatingshaft along the center of the stirring rotor, and the fourth reactor isa horizontal, approximately cylindrical vessel type reactor having aninlet and an outlet for a process solution at lower parts an one end andan another end in the longitudinal direction of the vessel,respectively, and an outlet for volatile matters at the upper part ofthe vessel, the reactor has two stirring rotors rotating in theproximity of the inside wall of the vessel in the longitudinal directionof the vessel, and the rotors each have stirring blades.
 15. A processaccording to claim 10 or 11, wherein a slurry of the aromaticdicarboxylic acid comprising terephthalic acid as a main ingredient or aderivative thereof and the glycol comprising 1,4-butanediol as a mainingredient prepared in a ratio of the former to the latter of 1:1.7 to1:3.0 is supplied to the first step upon admixture of an esterifyingcatalyst or a polymerization reaction catalyst.
 16. A process accordingto claim 11, wherein another third reactor or a plurality of thirdreactors is provided in parallel to the third reactor in the third step,thereby producing different polybutylene terephthalates having differentdegrees of polymerization from those produced in the third and fourthreactors of the main series of the third and fourth steps, or adjustingoperating conditions for each of the third reactors to control ofincrease in the product species, minute quality adjustment andproduction rate.